Time-lapse photography is a technique whereby the frequency at which film frames are captured is much lower than that used to view the sequence. When played at normal speed, time appears to be moving faster and thus lapsing.
In the past, time-lapse photography had employed a static camera position so that the background for a subject could be static and so a slowly changing subject could be readily viewed in a short period of time.
With the advent of hand-held image capture devices, it became desirable to produce time-lapse image sequences where the original background as well as the subject may have varied or moved within the captured images forming the sequence.
Instagram Hyperlapse is an application employing image stabilization techniques to smooth background movement within a scene as far as possible while a subject moves within the scene.
On the other hand, many users of mobile devices having front facing cameras routinely capture “selfie” images and wish to generate a time-lapse image sequence which maintains the subject, their face, at as large a size as possible and with the same location through the image sequence—while at the same time maintaining as much background imagery as possible so that the changing context for the subject can be appreciated.
These conflicting goals can make the computation required to process a set of source images with a mobile device to determine the optimal framing for images within a set of framed images unfeasibly onerous, especially when a large set of source images required to produce an interesting time-lapse image sequence may also contain a variety of images not necessarily conforming to the framing of other images or indeed not containing the same subject.